Breaking news! The corrosion of cold-rolled steel plates is really caused by dust!
I often receive inquiries about black spots on blanking sheets. According to macroeconomic and external economic conditions, it is judged to be rust, but I can't explain the cause. Later, I specially hired an expert in the field of corrosion to deal with this matter. After analysis, I finally understood the reason, and we will talk about it in detail below.
Situation: A customer reported that the raw material of cold-rolled DC03 was cut into pieces and left for two months, and many black spots the size of sharp pins were found on the surface. There is a light touch when touched hard, and some yellow halo can be seen vaguely on the edges of certain points.
This is actually a unique type of rust: spotty rust caused by dirt and grime.
Everyone has seen a lot of rust caused by water stains, so there is no need to talk about it.
The appearance of this kind of black spot rust requires two conditions: 1. The environment at the cutting and blanking line is poor and there is a lot of dust; 2. The air humidity on the day of cutting and blanking is high.
The moisture in the air uses dust particles as condensation water nuclei, forming partial water environment control in the dust. Fine water environment management can provide dissolved oxygen, an important substance that corrodes steel, thereby accelerating local corrosion of steel and producing "spot rust". Spot rust appears as many small pin-sized rust pits, mostly black in color, which will affect the subsequent coating and corrosion resistance of the finished product.
Dust plays two roles in this process: destroying the anti-rust oil slick, and collecting moisture in the air (condensation water nuclei).
You see, it has come full circle and comes back to the manufacturing organization and lean management. Therefore, make sure the warehouse is dry and clean on a daily basis.
